Setting parameter selected value for both Solution 1(star conected CT)Selected value for bothSolution 2 (delta connectedCT)ConnectTypeW1 Delta (D) STAR (Y) 1)ConnectTypeW2 star=y star=yClockNumberW2 1 [30 deg lag] 0 [0 deg] 1)ZSCurrSubtrW1 Off OffZSCurrSubtrW2 On On 2)TconfigForW1 No NoTconfigForW2 No NoLocationOLTC1 Not Used Not UsedOther parameters Not relevant for this application.Use default value.Not relevant for thisapplication. Use defaultvalue.1) To compensate for delta connected CTs.2) Zero-sequence current is already removed by connecting main CTs in delta.6.1.4.4 Summary and conclusions SEMOD168160-5 v3The IED can be used for differential protection of three-phase power transformerswith main CTs either star or delta connected. However the IED has been designedwith the assumption that all main CTS are star connected. The IED can be used inapplications where the main CTs are delta connected. For such applications thefollowing shall be kept in mind:1. The ratio for delta connected CTs shall be set √(3)=1.732 times smaller thanthe actual individual phase CT ratio.2. The power transformer vector group shall typically be set as Yy0 because thecompensation for power transformer the actual phase shift is provided by theexternal delta CT connection.3. The zero sequence current is eliminated by the main CT delta connections.Thus on sides where CTs are connected in delta the zero sequence currentelimination shall be set to Off in the IED.The following table summarizes the most commonly used star-delta vector groupsaround the world and provides information about the required type of main CTdelta connection on the star side of the protected transformer.1MRK 504 169-UEN A Section 6Differential protectionTransformer protection RET650 2.2 IEC 91Application manual
